Exemplos de Serialização de Dados Web Rust

// Web Rust JSON Serialization Examples
// Serialize Rust objects to JSON
//
// Add to Cargo.toml:
// [dependencies]
// serde = { version = "1.0", features = ["derive"] }
// serde_json = "1.0"

use serde::{Deserialize, Serialize, Serializer};
use serde_json::{json, to_string_pretty, Value};

// 1. Basic Serialization

/// Person struct with Serialize derive
#[derive(Debug, Serialize)]
struct Person {
    name: String,
    age: u32,
    email: String,
    active: bool,
}

/// Serialize struct to JSON string
fn serialize_to_json<T: Serialize>(value: &T) -> Result<String, serde_json::Error> {
    serde_json::to_string(value)
}

/// Serialize struct to pretty JSON string
fn serialize_to_pretty_json<T: Serialize>(value: &T) -> Result<String, serde_json::Error> {
    to_string_pretty(value)
}

// 2. Serialize Collections

/// Serialize vector to JSON array
fn serialize_vector(items: &[i32]) -> Result<String, serde_json::Error> {
    serde_json::to_string(items)
}

/// Serialize HashMap to JSON object
fn serialize_map(map: &std::collections::HashMap<String, String>) -> Result<String, serde_json::Error> {
    serde_json::to_string(map)
}

/// Serialize vector of structs
fn serialize_persons(persons: &[Person]) -> Result<String, serde_json::Error> {
    serde_json::to_string(persons)
}

// 3. Custom Serialization

/// Serialize with custom field names
#[derive(Debug, Serialize)]
struct User {
    #[serde(rename = "userId")]
    id: u32,
    #[serde(rename = "userName")]
    name: String,
    #[serde(rename = "userEmail")]
    email: String,
}

/// Serialize with conditionally skipped fields
#[derive(Debug, Serialize)]
struct Product {
    id: u32,
    name: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    description: Option<String>,
    #[serde(skip_serializing_if = "Vec::is_empty")]
    tags: Vec<String>,
    #[serde(skip_serializing)]
    internal_id: String,
}

// 4. Serialize Enums

/// Serialize simple enum
#[derive(Debug, Serialize)]
enum Status {
    Active,
    Inactive,
    Pending,
}

/// Serialize enum with data
#[derive(Debug, Serialize)]
enum Message {
    Text(String),
    Image { url: String, size: u32 },
    Video { url: String, duration: u32 },
}

/// Serialize enum with associated values
#[derive(Debug, Serialize)]
enum Response {
    Success(String),
    Error { code: u32, message: String },
    Empty,
}

// 5. Serialize with Custom Formatting

/// Serialize date as custom format
#[derive(Debug, Serialize)]
struct Event {
    name: String,
    #[serde(serialize_with = "serialize_date")]
    date: chrono::NaiveDate,
}

fn serialize_date<S>(date: &chrono::NaiveDate, serializer: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    let formatted = date.format("%Y-%m-%d").to_string();
    serializer.serialize_str(&formatted)
}

// 6. Serialize to Value

/// Serialize to generic JSON Value
fn serialize_to_value<T: Serialize>(value: &T) -> Result<Value, serde_json::Error> {
    serde_json::to_value(value)
}

/// Build JSON object dynamically
fn build_json_object(name: &str, age: u32, email: &str) -> Value {
    json!({
        "name": name,
        "age": age,
        "email": email,
        "created_at": "2024-01-15"
    })
}

/// Build JSON array dynamically
fn build_json_array(items: &[&str]) -> Value {
    json!(items)
}

// 7. Serialize with Transformation

/// Serialize with computed field
#[derive(Debug, Serialize)]
struct Invoice {
    items: Vec<InvoiceItem>,
    #[serde(skip_serializing)]
    tax_rate: f64,

    #[serde(serialize_with = "serialize_total")]
    total: f64,
}

#[derive(Debug, Serialize)]
struct InvoiceItem {
    name: String,
    quantity: u32,
    price: f64,
}

fn serialize_total<S>(total: &f64, serializer: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    let formatted = format!("{:.2}", total);
    serializer.serialize_str(&formatted)
}

// 8. Serialize Nested Structures

/// Serialize nested objects
#[derive(Debug, Serialize)]
struct Company {
    name: String,
    address: Address,
    employees: Vec<Employee>,
}

#[derive(Debug, Serialize)]
struct Address {
    street: String,
    city: String,
    country: String,
    postal_code: String,
}

#[derive(Debug, Serialize)]
struct Employee {
    id: u32,
    name: String,
    position: String,
    department: String,
}

// 9. Serialize Optional and Null

/// Serialize optional fields
#[derive(Debug, Serialize)]
struct Profile {
    username: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    bio: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    avatar_url: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    website: Option<String>,
}

// 10. Serialize with Custom Wrapper

/// Serialize with wrapper object
#[derive(Debug, Serialize)]
struct ApiResponse<T> {
    success: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    message: Option<String>,
    data: T,
}

/// Create API response wrapper
fn create_response<T: Serialize>(data: T, message: Option<String>) -> ApiResponse<T> {
    ApiResponse {
        success: true,
        message,
        data,
    }
}

// Usage Examples
fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("=== Web Rust JSON Serialization Examples ===\n");

    // 1. Basic serialization
    println!("--- 1. Basic Serialization ---");
    let person = Person {
        name: "Alice".to_string(),
        age: 30,
        email: "[email protected]".to_string(),
        active: true,
    };
    println!("Serialized: {}", serialize_to_json(&person)?);
    println!("Pretty:\n{}", serialize_to_pretty_json(&person)?);

    // 2. Serialize collections
    println!("\n--- 2. Serialize Collections ---");
    let numbers = vec![1, 2, 3, 4, 5];
    println!("Vector: {}", serialize_vector(&numbers)?);

    let mut map = std::collections::HashMap::new();
    map.insert("key1".to_string(), "value1".to_string());
    map.insert("key2".to_string(), "value2".to_string());
    println!("Map: {}", serialize_map(&map)?);

    // 3. Custom field names
    println!("\n--- 3. Custom Field Names ---");
    let user = User {
        id: 1,
        name: "Bob".to_string(),
        email: "[email protected]".to_string(),
    };
    println!("User: {}", serialize_to_pretty_json(&user)?);

    // 4. Conditional serialization
    println!("\n--- 4. Conditional Serialization ---");
    let product = Product {
        id: 1,
        name: "Laptop".to_string(),
        description: Some("High-performance laptop".to_string()),
        tags: vec!["electronics".to_string(), "computers".to_string()],
        internal_id: "INT-123".to_string(),
    };
    println!("Product: {}", serialize_to_pretty_json(&product)?);

    // 5. Serialize enums
    println!("\n--- 5. Serialize Enums ---");
    let status = Status::Active;
    println!("Status: {}", serialize_to_json(&status)?);

    let message = Message::Image {
        url: "https://example.com/image.jpg".to_string(),
        size: 1024,
    };
    println!("Message: {}", serialize_to_json(&message)?);

    // 6. Dynamic JSON
    println!("\n--- 6. Dynamic JSON ---");
    let obj = build_json_object("Charlie", 25, "[email protected]");
    println!("Dynamic object: {}", to_string_pretty(&obj)?);

    let arr = build_json_array(&["apple", "banana", "orange"]);
    println!("Dynamic array: {}", to_string_pretty(&arr)?);

    // 7. Nested structures
    println!("\n--- 7. Nested Structures ---");
    let company = Company {
        name: "Tech Corp".to_string(),
        address: Address {
            street: "123 Main St".to_string(),
            city: "San Francisco".to_string(),
            country: "USA".to_string(),
            postal_code: "94102".to_string(),
        },
        employees: vec![
            Employee {
                id: 1,
                name: "Alice".to_string(),
                position: "Developer".to_string(),
                department: "Engineering".to_string(),
            },
        ],
    };
    println!("Company: {}", serialize_to_pretty_json(&company)?);

    // 8. Optional fields
    println!("\n--- 8. Optional Fields ---");
    let profile = Profile {
        username: "alice".to_string(),
        bio: Some("Software developer".to_string()),
        avatar_url: None,
        website: Some("https://alice.dev".to_string()),
    };
    println!("Profile: {}", serialize_to_pretty_json(&profile)?);

    // 9. API response wrapper
    println!("\n--- 9. API Response Wrapper ---");
    let response = create_response(
        person,
        Some("User retrieved successfully".to_string()),
    );
    println!("API Response: {}", serialize_to_pretty_json(&response)?);

    // 10. Custom transformation
    println!("\n--- 10. Custom Transformation ---");
    let invoice = Invoice {
        items: vec![
            InvoiceItem {
                name: "Service A".to_string(),
                quantity: 2,
                price: 100.0,
            },
        ],
        tax_rate: 0.1,
        total: 220.0,
    };
    println!("Invoice: {}", serialize_to_pretty_json(&invoice)?);

    println!("\n=== All JSON Serialization Examples Completed ===");
    Ok(())
}

// Web Rust JSON Deserialization Examples
// Deserialize JSON strings to Rust objects
//
// Add to Cargo.toml:
// [dependencies]
// serde = { version = "1.0", features = ["derive"] }
// serde_json = "1.0"

use serde::{Deserialize, Serialize, Deserializer};
use serde_json::{from_str, Value};
use std::collections::HashMap;

// 1. Basic Deserialization

/// Person struct with Deserialize derive
#[derive(Debug, Deserialize, Serialize)]
struct Person {
    name: String,
    age: u32,
    email: String,
    active: bool,
}

/// Deserialize JSON string to struct
fn deserialize_from_json<T: for<'de> Deserialize<'de>>(json: &str) -> Result<T, serde_json::Error> {
    from_str(json)
}

// 2. Deserialize Collections

/// Deserialize JSON array to vector
fn deserialize_to_vector(json: &str) -> Result<Vec<i32>, serde_json::Error> {
    from_str(json)
}

/// Deserialize JSON object to HashMap
fn deserialize_to_map(json: &str) -> Result<HashMap<String, String>, serde_json::Error> {
    from_str(json)
}

/// Deserialize JSON array of objects
fn deserialize_to_persons(json: &str) -> Result<Vec<Person>, serde_json::Error> {
    from_str(json)
}

// 3. Flexible Deserialization

/// Deserialize struct with optional fields
#[derive(Debug, Deserialize)]
struct UserProfile {
    username: String,
    #[serde(default)]
    bio: String,
    #[serde(default)]
    avatar_url: Option<String>,
    #[serde(default)]
    active: bool,
}

/// Deserialize struct with default values
#[derive(Debug, Deserialize)]
struct Config {
    #[serde(default = "default_port")]
    port: u16,
    #[serde(default)]
    host: String,
    #[serde(default = "default_timeout")]
    timeout: u64,
}

fn default_port() -> u16 { 8080 }
fn default_timeout() -> u64 { 30 }

// 4. Custom Field Names

/// Deserialize with renamed fields
#[derive(Debug, Deserialize)]
struct ApiUser {
    #[serde(rename = "userId")]
    id: u32,
    #[serde(rename = "userName")]
    name: String,
    #[serde(rename = "userEmail")]
    email: String,
}

// 5. Deserialize Enums

/// Deserialize simple enum
#[derive(Debug, Deserialize, Serialize)]
enum Status {
    Active,
    Inactive,
    Pending,
}

/// Deserialize enum with data
#[derive(Debug, Deserialize, Serialize)]
enum Message {
    Text(String),
    Image { url: String, size: u32 },
    Video { url: String, duration: u32 },
}

// 6. Deserialize with Validation

/// Deserialize age with validation
fn deserialize_age<'de, D>(deserializer: D) -> Result<u32, D::Error>
where
    D: Deserializer<'de>,
{
    let age = u32::deserialize(deserializer)?;
    if age > 150 {
        return Err(serde::de::Error::custom("Age must be <= 150"));
    }
    Ok(age)
}

#[derive(Debug, Deserialize)]
struct ValidatedPerson {
    name: String,
    #[serde(deserialize_with = "deserialize_age")]
    age: u32,
    email: String,
}

// 7. Deserialize to Dynamic Value

/// Deserialize to generic Value
fn deserialize_to_value(json: &str) -> Result<Value, serde_json::Error> {
    from_str(json)
}

/// Extract field from JSON
fn extract_field(json: &str, field: &str) -> Option<Value> {
    let v: Value = from_str(json).ok()?;
    v.get(field).cloned()
}

/// Extract nested field
fn extract_nested_field(json: &str, path: &[&str]) -> Option<Value> {
    let mut v: Value = from_str(json).ok()?;
    for key in path {
        v = v.get(key)?.clone();
    }
    Some(v)
}

// 8. Deserialize with Transformation

/// Deserialize and transform date string
fn deserialize_date<'de, D>(deserializer: D) -> Result<chrono::NaiveDate, D::Error>
where
    D: Deserializer<'de>,
{
    let s = String::deserialize(deserializer)?;
    chrono::NaiveDate::parse_from_str(&s, "%Y-%m-%d")
        .map_err(serde::de::Error::custom)
}

#[derive(Debug, Deserialize)]
struct Event {
    name: String,
    #[serde(deserialize_with = "deserialize_date")]
    date: chrono::NaiveDate,
}

// 9. Deserialize Enums with Tag

/// Deserialize enum with type tag
#[derive(Debug, Deserialize, Serialize)]
enum Animal {
    Dog { name: String, breed: String },
    Cat { name: String, indoor: bool },
    Bird { name: String, can_fly: bool },
}

// 10. Error Handling

/// Deserialize with helpful error message
fn deserialize_safe<T: for<'de> Deserialize<'de>>(json: &str) -> Result<T, String> {
    from_str(json).map_err(|e| format!("Failed to deserialize: {}", e))
}

/// Try multiple formats
fn deserialize_flexibly<T: for<'de> Deserialize<'de>>(json: &str) -> Result<T, String> {
    // Try standard format
    if let Ok(result) = from_str(json) {
        return Ok(result);
    }

    // Try with relaxed rules
    // Add more fallback logic here if needed

    Err("All deserialization attempts failed".to_string())
}

// Usage Examples
fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("=== Web Rust JSON Deserialization Examples ===\n");

    // 1. Basic deserialization
    println!("--- 1. Basic Deserialization ---");
    let json_person = r#"{"name":"Alice","age":30,"email":"[email protected]","active":true}"#;
    let person: Person = deserialize_from_json(json_person)?;
    println!("Deserialized: {:?}", person);

    // 2. Deserialize collections
    println!("\n--- 2. Deserialize Collections ---");
    let json_array = r#"[1,2,3,4,5]"#;
    let numbers: Vec<i32> = deserialize_to_vector(json_array)?;
    println!("Numbers: {:?}", numbers);

    let json_object = r#"{"key1":"value1","key2":"value2"}"#;
    let map: HashMap<String, String> = deserialize_to_map(json_object)?;
    println!("Map: {:?}", map);

    // 3. Optional fields
    println!("\n--- 3. Optional Fields ---");
    let json_profile = r#"{"username":"alice","active":true}"#;
    let profile: UserProfile = deserialize_from_json(json_profile)?;
    println!("Profile: {:?}", profile);

    // 4. Default values
    println!("\n--- 4. Default Values ---");
    let json_config = r#"{"host":"localhost"}"#;
    let config: Config = deserialize_from_json(json_config)?;
    println!("Config: {:?}", config);

    // 5. Renamed fields
    println!("\n--- 5. Renamed Fields ---");
    let json_user = r#"{"userId":1,"userName":"Bob","userEmail":"[email protected]"}"#;
    let user: ApiUser = deserialize_from_json(json_user)?;
    println!("User: {:?}", user);

    // 6. Enums
    println!("\n--- 6. Deserialize Enums ---");
    let json_status = r#""Active""#;
    let status: Status = deserialize_from_json(json_status)?;
    println!("Status: {:?}", status);

    // 7. Dynamic value
    println!("\n--- 7. Dynamic Value ---");
    let json_dynamic = r#"{"name":"Charlie","age":25,"city":"NYC"}"#;
    let v: Value = deserialize_to_value(json_dynamic)?;
    println!("Value: {}", v);

    if let Some(name) = extract_field(json_dynamic, "name") {
        println!("Extracted name: {}", name);
    }

    // 8. Validation
    println!("\n--- 8. Validation ---");
    let json_valid = r#"{"name":"David","age":30,"email":"[email protected]"}"#;
    match deserialize_from_json::<ValidatedPerson>(json_valid) {
        Ok(person) => println!("Valid person: {:?}", person),
        Err(e) => println!("Error: {}", e),
    }

    // 9. Transformation
    println!("\n--- 9. Transformation ---");
    let json_event = r#"{"name":"Conference","date":"2024-06-15"}"#;
    let event: Event = deserialize_from_json(json_event)?;
    println!("Event: {:?}", event);

    // 10. Error handling
    println!("\n--- 10. Error Handling ---");
    let invalid_json = r#"{"invalid":"data"}"#;
    match deserialize_safe::<Person>(invalid_json) {
        Ok(person) => println!("Person: {:?}", person),
        Err(e) => println!("Error: {}", e),
    }

    println!("\n=== All JSON Deserialization Examples Completed ===");
    Ok(())
}

// Web Rust XML Parsing Examples
// Parse and manipulate XML documents
//
// Add to Cargo.toml:
// [dependencies]
// quick-xml = "0.31"

use quick_xml::events::{Event, BytesDecl, BytesStart, BytesEnd, BytesText};
use quick_xml::Writer;
use std::io::Cursor;

// 1. Basic XML Parsing

/// Parse XML and extract element content
fn parse_element_content(xml: &str, element_name: &str) -> Result<Option<String>, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut in_element = false;
    let mut content = None;

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Start(ref e) => {
                if e.name().as_ref() == element_name.as_bytes() {
                    in_element = true;
                }
            }
            Event::Text(e) if in_element => {
                content = Some(e.unescape()?.into_owned());
            }
            Event::End(ref e) => {
                if e.name().as_ref() == element_name.as_bytes() {
                    in_element = false;
                    break;
                }
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(content)
}

/// Extract all elements with specific tag
fn extract_elements(xml: &str, tag: &str) -> Result<Vec<String>, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut elements = Vec::new();
    let mut in_target = false;

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Start(ref e) => {
                if e.name().as_ref() == tag.as_bytes() {
                    in_target = true;
                }
            }
            Event::Text(e) if in_target => {
                elements.push(e.unescape()?.into_owned());
            }
            Event::End(ref e) => {
                if e.name().as_ref() == tag.as_bytes() {
                    in_target = false;
                }
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(elements)
}

// 2. Parse XML Attributes

/// Extract attributes from an element
fn extract_attributes(xml: &str, element: &str) -> Result<Vec<(String, String)>, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut attributes = Vec::new();
    let mut buf = Vec::new();

    let mut reader = reader;
    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Start(e) => {
                if e.name().as_ref() == element.as_bytes() {
                    for attr in e.attributes() {
                        let attr = attr?;
                        let key = std::str::from_utf8(attr.key.as_ref())?.to_string();
                        let value = attr.unescape_value()?.to_string();
                        attributes.push((key, value));
                    }
                    break;
                }
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(attributes)
}

// 3. Parse Nested Structures

/// Person struct parsed from XML
#[derive(Debug)]
struct Person {
    name: String,
    age: u32,
    email: String,
}

/// Parse person from XML
fn parse_person(xml: &str) -> Result<Person, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut current_element = String::new();
    let mut name = String::new();
    let mut age = String::new();
    let mut email = String::new();

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Start(e) => {
                current_element = std::str::from_utf8(e.name().as_ref())?.to_string();
            }
            Event::Text(e) => {
                match current_element.as_str() {
                    "name" => name = e.unescape()?.into_owned(),
                    "age" => age = e.unescape()?.into_owned(),
                    "email" => email = e.unescape()?.into_owned(),
                    _ => {}
                }
            }
            Event::End(_) => {
                current_element.clear();
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(Person {
        name,
        age: age.parse()?,
        email,
    })
}

// 4. Build XML

/// Create simple XML element
fn build_element(name: &str, content: &str) -> Result<String, Box<dyn std::error::Error>> {
    let mut writer = Writer::new(Cursor::new(Vec::new()));
    writer.write_event(Event::Start(BytesStart::new(name)))?;
    writer.write_event(Event::Text(BytesText::new(content)))?;
    writer.write_event(Event::End(BytesEnd::new(name)))?;

    let result = writer.into_inner().into_inner();
    Ok(String::from_utf8(result)?)
}

/// Create XML with attributes
fn build_element_with_attrs(
    name: &str,
    attrs: &[(&str, &str)],
    content: &str,
) -> Result<String, Box<dyn std::error::Error>> {
    let mut writer = Writer::new(Cursor::new(Vec::new()));

    let mut elem = BytesStart::new(name);
    for (key, value) in attrs {
        elem.push_attribute((*key, *value));
    }

    writer.write_event(Event::Start(elem))?;
    writer.write_event(Event::Text(BytesText::new(content)))?;
    writer.write_event(Event::End(BytesEnd::new(name)))?;

    let result = writer.into_inner().into_inner();
    Ok(String::from_utf8(result)?)
}

// 5. XML to Struct Conversion

/// Book struct
#[derive(Debug)]
struct Book {
    title: String,
    author: String,
    year: u32,
}

/// Parse book from XML
fn parse_book(xml: &str) -> Result<Book, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut current = String::new();
    let mut title = String::new();
    let mut author = String::new();
    let mut year = String::new();

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Start(e) => {
                current = std::str::from_utf8(e.name().as_ref())?.to_string();
            }
            Event::Text(e) => {
                match current.as_str() {
                    "title" => title = e.unescape()?.into_owned(),
                    "author" => author = e.unescape()?.into_owned(),
                    "year" => year = e.unescape()?.into_owned(),
                    _ => {}
                }
            }
            Event::End(_) => current.clear(),
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(Book {
        title,
        author,
        year: year.parse()?,
    })
}

// 6. Serialize to XML

/// Convert book to XML
fn book_to_xml(book: &Book) -> Result<String, Box<dyn std::error::Error>> {
    let mut writer = Writer::new_with_indent(Cursor::new(Vec::new()), b' ', 4);

    writer.write_event(Event::Decl(BytesDecl::new("1.0", Some("UTF-8"), None)))?;

    let mut root = BytesStart::new("book");
    writer.write_event(Event::Start(root))?;

    let mut title_elem = BytesStart::new("title");
    writer.write_event(Event::Start(title_elem))?;
    writer.write_event(Event::Text(BytesText::new(&book.title)))?;
    writer.write_event(Event::End(BytesEnd::new("title")))?;

    let mut author_elem = BytesStart::new("author");
    writer.write_event(Event::Start(author_elem))?;
    writer.write_event(Event::Text(BytesText::new(&book.author)))?;
    writer.write_event(Event::End(BytesEnd::new("author")))?;

    let mut year_elem = BytesStart::new("year");
    writer.write_event(Event::Start(year_elem))?;
    writer.write_event(Event::Text(BytesText::new(&book.year.to_string())))?;
    writer.write_event(Event::End(BytesEnd::new("year")))?;

    writer.write_event(Event::End(BytesEnd::new("book")))?;

    let result = writer.into_inner().into_inner();
    Ok(String::from_utf8(result)?)
}

// 7. Extract CDATA

/// Extract CDATA content
fn extract_cdata(xml: &str) -> Result<Option<String>, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut cdata_content = None;

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::CData(e) => {
                cdata_content = Some(e.to_string());
                break;
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(cdata_content)
}

// 8. Extract Comments

/// Extract all XML comments
fn extract_comments(xml: &str) -> Result<Vec<String>, Box<dyn std::error::Error>> {
    let reader = quick_xml::Reader::from_str(xml);
    let mut comments = Vec::new();

    let mut reader = reader;
    let mut buf = Vec::new();

    loop {
        match reader.read_event_into(&mut buf)? {
            Event::Comment(e) => {
                comments.push(e.to_string());
            }
            Event::Eof => break,
            _ => {}
        }
        buf.clear();
    }

    Ok(comments)
}

// 9. Build Complex XML

/// Build nested XML structure
fn build_catalog_xml(books: &[Book]) -> Result<String, Box<dyn std::error::Error>> {
    let mut writer = Writer::new_with_indent(Cursor::new(Vec::new()), b' ', 2);

    writer.write_event(Event::Decl(BytesDecl::new("1.0", Some("UTF-8"), None)))?;

    let mut catalog = BytesStart::new("catalog");
    writer.write_event(Event::Start(catalog))?;

    for book in books {
        let mut book_elem = BytesStart::new("book");
        writer.write_event(Event::Start(book_elem))?;

        // Title
        let mut title = BytesStart::new("title");
        writer.write_event(Event::Start(title))?;
        writer.write_event(Event::Text(BytesText::new(&book.title)))?;
        writer.write_event(Event::End(BytesEnd::new("title")))?;

        // Author
        let mut author = BytesStart::new("author");
        writer.write_event(Event::Start(author))?;
        writer.write_event(Event::Text(BytesText::new(&book.author)))?;
        writer.write_event(Event::End(BytesEnd::new("author")))?;

        // Year
        let mut year = BytesStart::new("year");
        writer.write_event(Event::Start(year))?;
        writer.write_event(Event::Text(BytesText::new(&book.year.to_string())))?;
        writer.write_event(Event::End(BytesEnd::new("year")))?;

        writer.write_event(Event::End(BytesEnd::new("book")))?;
    }

    writer.write_event(Event::End(BytesEnd::new("catalog")))?;

    let result = writer.into_inner().into_inner();
    Ok(String::from_utf8(result)?)
}

// Usage Examples
fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("=== Web Rust XML Parsing Examples ===\n");

    // 1. Parse element content
    println!("--- 1. Parse Element Content ---");
    let xml = r#"<root><greeting>Hello, World!</greeting></root>"#;
    match parse_element_content(xml, "greeting") {
        Ok(Some(content)) => println!("Greeting: {}", content),
        _ => println!("Not found"),
    }

    // 2. Extract all elements
    println!("\n--- 2. Extract All Elements ---");
    let xml = r#"<root><item>Apple</item><item>Banana</item><item>Orange</item></root>"#;
    let items = extract_elements(xml, "item")?;
    println!("Items: {:?}", items);

    // 3. Extract attributes
    println!("\n--- 3. Extract Attributes ---");
    let xml = r#"<person id="1" name="Alice" age="30" />"#;
    let attrs = extract_attributes(xml, "person")?;
    println!("Attributes: {:?}", attrs);

    // 4. Parse person
    println!("\n--- 4. Parse Structured Data ---");
    let xml = r#"
        <person>
            <name>Bob</name>
            <age>25</age>
            <email>bob@example.com</email>
        </person>
    "#;
    let person = parse_person(xml)?;
    println!("Person: {:?}", person);

    // 5. Build XML
    println!("\n--- 5. Build XML ---");
    let xml = build_element("message", "Hello, XML!")?;
    println!("Simple element: {}", xml);

    let xml_with_attrs = build_element_with_attrs(
        "user",
        &[("id", "1"), ("name", "Alice")],
        "Content",
    )?;
    println!("With attributes: {}", xml_with_attrs);

    // 6. Parse and build book
    println!("\n--- 6. Book Serialization ---");
    let xml = r#"<book><title>Rust Programming</title><author>Steve Klabnik</author><year>2023</year></book>"#;
    let book = parse_book(xml)?;
    println!("Parsed book: {:?}", book);

    let book_xml = book_to_xml(&book)?;
    println!("Serialized:\n{}", book_xml);

    // 7. Build catalog
    println!("\n--- 7. Build Complex XML ---");
    let books = vec![
        Book {
            title: "The Rust Book".to_string(),
            author: "Steve Klabnik".to_string(),
            year: 2023,
        },
        Book {
            title: "Programming Rust".to_string(),
            author: "Jim Blandy".to_string(),
            year: 2021,
        },
    ];
    let catalog_xml = build_catalog_xml(&books)?;
    println!("Catalog:\n{}", catalog_xml);

    println!("\n=== All XML Parsing Examples Completed ===");
    Ok(())
}